The invention relates to improvements in a mechanism and method of continuously making thermoplastic film having fastener profiles on the surface thereof and more particularly wherein the temperature of the plastic for the profiles and film, and the delivery of the plastic can be individually controlled and wherein the dimensions of the film and the location of the profiles can be rapidly and simply changed without requiring additional separate die heads.
This type of thermoplastic film with fastener profiles on the surface is used for lightweight reclosable bags which vary in size and gauge in accordance with the product to be packaged therein and also vary in that the original bags may be open at the bottom or at the top depending upon the contents and the filling procedure used. To form these bags a thin thermoplastic film is first extruded in a continuous film length with fastener profiles on the surface. After cooling the film is then folded by being doubled along its center so that the fastener profiles are brought together, and the fastener profiles may be pressed together to be joined or left separated. The bags are formed by cross-sealing and cross-cutting the film in predetermined lengths dependent upon the width of the bag to be obtained. The height of the bag is determined by the width of the film sheet which is extruded, and the location of the fastener profiles is determined by their position relative to the edge of the film. Should a bottom open bag be desired, the profiles will be placed near the center of the film and the height of the bag will be determined by the distance from the profiles to the edge of the film. The film is produced from various types of thermoplastic resins or combinations of same such as, for example, polyethylene (high or low density), polypropylene, polystyrene, polyvinyl chloride (hard and soft), polyvinylidine chloride, cellulose acetate, polyesters, etc. The plastic is chosen to have optimum characteristics for the bag usually requiring clarity and resiliency, or in the case of combined (coextruded) films for their different barrier properties. By separately extruding the profiles and attaching them in the fused state, plastic of optimum characteristics for the profiles can be chosen substantially independent of the plastic of the bag. For example, a more stiff, and slippery plastic is better suited to the formation of profiles to the bag material. Also, plastic of different colors may be employed. After the profiles and film are brought together in the fusible state, they are subjected to cooling.
In certain instances, it may be desirable to form a sheet of plastic with a single profile extending therealong. Such a sheet can be utilized, for example, in the forming of bags by placing it in face-to-face relationship with another sheet with the profiles in alignment, and the sheets sealed along the side and bottom edges to form an open bag.
It is accordingly an object of the present invention to provide an improved mechanism and method for extrusion of a film and extrusion of profiles positioned on the surface wherein the location of the profiles relative to the width of the plastic sheet can be quickly, easily and simply changed without requiring the exchange of die heads and other equipment and hence the necessity of a large stock of dies to accommodate the many bag heights required.
A further object of the invention is to provide an improved plastic extrusion mechanism of the type described wherein a greater dexterity is obtainable in the control of the temperature and amount of plastic delivered to the film extrusion slot and the profile extrusion openings to thereby improve the quality of the product obtained therefrom.
A still further object of the invention is to provide an extrusion mechanism for providing profile sheets wherein the various demands of different types of bags can be readily and quickly accommodated without any great loss in downtime such as those affecting the width of the sheet, the location of the profiles and the nature and conditions of extrusion of the plastic.
A further object of the invention is to provide a method of and apparatus for extruding a sheet and attaching a single profile or a plurality of profiles thereto, and more easily controlling the location of the profile or profiles relative to the edge of the sheet;
Other objects, advantages and features will become more apparent, as will equivalent methods and mechanisms which are intended to be covered herein, from the teaching of the principles of the invention in the description of the preferred embodiments of the specification, claims and drawings, in which: